A starter head comprises a starter pinion which is displaceable axially on a motor shaft until it comes into mesh with a toothed crown carried by the engine flywheel. A free wheel and a driving sleeve are associated with the starter pinion, to which they are secured by means of a shroud. The driving sleeve includes at one of its ends helical splines which cooperate with further helical splines formed on the motor shaft, so that the whole of the starter head is rotatable with respect to the motor shaft.
The axial displacement, or throw, of the head is limited by a throw limiting device, which generally comprises a ring carried on the free end of the motor shaft by the side of the toothed crown which cooperates with the end of the starter pinion in the working position, that is to say in the position in which the pinion is in mesh with the toothed crown. A configuration of this type requires a portion of the motor shaft to project beyond the starter pinion, and even to project out of the casing of the starter assembly itself. This makes it both difficult and costly to provide an effective protection for the projecting portion of the motor shaft against foreign matter and/or other mechanical influences in the environment in which the starter has to operate.
In order to overcome this drawback, a throw limiting device is incorporated in the starter head. This throw limiting device generally operates by cooperation of the ends of the helical grooves formed on the driving sleeve of the head and the motor shaft. The disadvantages of such a device become evident on fitting the starter head on to the motor shaft.
In this connection, the head itself is no longer a simple assembly which can be fitted on the motor shaft, the rear portion of which has previously been fitted with the armature of the electric starter motor. It is therefore necessary in practice to introduce the driving sleeve of the starter head through this rear portion, the motor armature then being assembled on the shaft, and the various components of the starter head being finally assembled in situ. It is practically impossible to carry out such a manufacturing process automatically, with the result that assembly of the starter involves major additional costs.